1. Field of the Invention
The present invention relates to a liquid crystal display device, and particularly, to a liquid crystal display device having high brightness.
2. Description of the Related Art
Recently, as more and more portable electronic instruments, such as mobile phones, PDAs, notebook computers, and the like are being developed, lighter and more compact flat panel display devices capable of being used in these instruments have been required. As the demand for these flat panel display devices increases, more research as in LCD (Liquid Crystal Display), PDP (Plasma Display Panel), FED (Field Emission Display), VFD (Vacuum Fluorescent Display) and the like are actively being carried out. Considering such aspects as mass production capability, display driving ease, and high image quality, the LCD device is the display device among the flat panel display devices that is currently receiving the most attention.
In general, the LCD device is designed to display desired images by individually providing a data signal according to image information to pixels arranged in matrix. The data signals adjusts the light transmissivity of the pixels. FIG. 1 shows a cross-sectional view of a related art LCD device. As shown in FIG. 1, the LCD device includes a liquid crystal panel 1 having pixels arranged in matrix and a backlight assembly 2 for irradiating light onto the liquid crystal panel 1.
The liquid crystal panel 1 includes a TFT (Thin Film Transistor) array substrate 3 and a color filter substrate 5, which face each other and are attached to each other with a cell gap between them. A liquid crystal layer 7 fills the cell gap between the TFT array substrate 3 and the color filter substrate 5.
Although not shown in FIG. 1, a plurality of pixels are defined by gate lines and data lines on the TFT array substrate 3. A driving device, such as a thin film transistor 9, is formed in each pixel. A black matrix 11 is formed on the color filter substrate 3 to prevent light leakage in the regions where the gate lines, the data lines and the thin film transistor 9 are located. A color filter layer 13 having red, green, and blue filters for producing the full color spectrum is formed in the black matrix 11 of the color filter substrate.
The TFT array substrate 3 and the color filter substrate 5 respectively have a pixel electrode and a common electrode. Alignment layers 19a and 19b for aligning liquid crystal molecules are coated on the TFT array substrate 3 and the color filter substrate 5, respectively. The TFT array substrate 3 and the color filter substrate 5 are attached to each other by a sealing material 21. Lower and upper polarizers 23a and 23b for polarizing light coming out of the backlight assembly are formed on upper and rear surfaces of the liquid crystal panel 1, respectively.
The LCD device is a light receiving display device having the characteristic of displaying images by adjusting light transmission through the device without emitting light by itself. Thus, a separate unit for irradiating light onto the liquid crystal panel 1, namely, a backlight assembly 2 is provided at the rear surface of the liquid crystal panel 1. A light source 25 of the backlight assembly 2 is installed at a side surface of a light-guiding plate 27, a reflection sheet 29 is positioned at the rear surface of the light-guiding plate 27, and an optical sheet 31 is laminated on the light-guiding plate 27. Therefore, light irradiated from the light source 25 is condensed by the light-guiding plate 27 and passes through the optical sheets 31, including a diffusion sheet and a prism sheet. Thereafter, the light is irradiated onto the region of the liquid crystal panel 1 of the LCD device as indicated with arrow i in FIG. 1. As a result, characters or images can be displayed using the light passing through the liquid crystal panel 1.
In the color filter type LCD device according to the related art, most light i irradiated from the backlight assembly 2 is substantially absorbed or blocked. However, some light iii passes through the lower TFT array substrate 3, elements of the upper color filter substrate 5 and the liquid crystal layer 7, sequentially, as a part of the display. Only as much as about 3% to 5% of the initially irradiated light is displayed. Thus, the light efficiency is very low.